make qual_handling enum for canonicalize() public

[f-cozzocrea]

Applies the change made to the aro source in ziglang/zig#19227.

[Vexu]

Looks like the new pointer safety checks found a bug, I'll look into it tomorrow.

[ehaas]

Repro:

const std = @import("std");
test "Allocation failures" {
    const Test = struct {
        fn testOne(allocator: std.mem.Allocator) !void {
            var map: std.StringHashMapUnmanaged(void) = .{};
            defer map.deinit(allocator);

            _ = try map.getOrPut(allocator, "hello");
        }
    };

    try std.testing.checkAllAllocationFailures(std.testing.allocator, Test.testOne, .{});
}

[ehaas]

Upstream bug report ziglang/zig#19358